Shelf Sea Biogeochemistry blog

Saturday, 22 August 2015

Collecting images from the seafloor.

We have completed sediment core sampling at our
four main study sites. This is a key achievement for the trip. We are
now sampling one other site that allows us to cross-reference our
findings with those of other studies and a long-term
study station with the nickname Candyfloss. This site is closer to the
continental shelf edge and open ocean than we have been for most of the
trip. Marine life spotting has been good and we even laid eyes on the RRS James Cook about ten miles from us. The James Cook isresearching life in the canyons that extend just beyond the shelf edge. We will soon return northward to for the more AUV deployments, the fourth deployment of the NOC lander,
as well as a few other remaining tasks.

We are using the Autsub3 autonomous underwater vehicle (AUV) during our cruise to collect photographic images of the
seafloor, as well as sonar-based images of the shape and texture of the
seafloor. We have been running the AUV in a ‘mowing
the lawn’ pattern of parallel lines that are about ~5km long. After
checking our seafloor shape and texture mapping for any obstacles, we
‘fly’ the AUV as close as 2.5 meters from the seafloor to collect colour
photographs in the moderately cloudy waters of
the Celtic Sea.

The images will be geo-referenced, which
effectively turns the photo into a map like you see in Google Earth. As
you can see below, that 2.5 m height above the seafloor still gives us
images that are very useful for determining the identity
size, and location of all the observed images. This can provide a
landscape scale view of the seafloor and its inhabitants, which we can
then use to improve estimates of ecological and biogeochemical patterns
and processes.

The seafloor and its inhabitants

AUV photographs are particularly useful in
estimating the distribution of biomass of larger animals that are not
sampled well by trawls or sediment cores. Observed animals include
crabs, shrimps, and anemones as well as fish. The images
above and below come from a Celtic Sea site where the seafloor is dominated by
sandy mud.